Glass sheets are heated while conveyed along a horizontally disposed roller conveyor that comprises rolls that rotate in unison to move a series of glass sheets through an enclosed furnace. The conveyor rolls have ends that project outwardly through openings in the furnace housing. These openings are closed as securely as possible by directly engaging the rolls adjacent their ends with insulation to prevent heat loss from the furnace and to prevent relatively cool ambient air from entering the furnace and causing thermal distortion of conveyed glass sheets. The relatively tightly sealed relationship provided by the roll contacting seals also protects the exterior of the furnace from becoming too hot for operator comfort.
In an apparatus for tempering glass sheets, the horizontal conveyor extends through a furnace having exit openings and entrance openings and the flow of air into and out of the furnace has been controlled by incorporating air locks with exit and entrance doors which are opened and closed in an alternating manner to maintain a superatmospheric pressure within the air locks protecting the furnace so as to minimize the loss of hot air from the furnace through the entrance and exit openings. Also, upper and lower sets of compressible rolls separated by approximately the glass sheet thickness have been used to reduce leakage at the entrance and exit openings of furnaces where flat sheets are heated for tempering.
When glass sheets are shaped to complicated shapes and tempered, it is expedient to use a movable vacuum holder within a furnace to support and convey the glass sheet after it has been heated to a processing temperature and while it is conveyed to a shaping station. The holder utilizes shuttle means outside the furnace to control movement of the holder within the furnace and a vacuum source outside the furnace to supply vacuum to the holder through one or more vacuum supply pipes. Frame members connecting the holder to the shuttle means and vacuum supply pipes connecting the vacuum holder to the vacuum source necessarily are movable with the glass sheet holder. The connecting frame members, through which the holder is connected to shuttle means and the vacuum supply pipes connecting the vacuum holder to a vacuum source, extend through the side walls of the enclosed heating furnace. Therefore, the furnace walls must be provided with elongated slots to permit movement of connecting means members such as the connecting frame members and the vacuum supply pipes to the holder supported by the shuttle. An elongated opening along the length of the side wall equal in length to the distance that must be traveled by the shuttle leaves a large space through which hot air can escape.
The prior art lacks means to seal the entire length of such an elongated opening to prevent loss of furnace heat through the opening and also open locally for only the minimum space and time needed to allow each connecting means member to pass through each local portion of the elongated opening and to reseal the local open portion when said connecting frame member and/or vacuum supply line passes said local portion.